This application claims the priority of Italian Application No. BO2001A 000092 filed Feb. 20, 2001, the disclosure of which is being incorporated herein by reference.
The present invention concerns an electrohydraulic device for operating the valves of a combustion engine.
As is known, combustion engines are currently being tested out in which the intake and exhaust valves that selectively establish communication between the engine combustion chamber and the engine intake and exhaust manifolds respectively are operated by electrohydraulic devices driven by an electronic control unit.
This solution permits very accurate variation of the opening and closing moments of the valves according to the angular speed of the crankshaft and other engine operating parameters, considerably increasing engine efficiency.
In greater detail, combustion engines are currently being tested out provided with an electrohydraulic operating device for each engine intake and/or exhaust valve; said device comprises a linear hydraulic actuator designed to move the valve axially from the closed position to the maximum opening position, overcoming the action of an elastic element designed to maintain the valve in the closed position, and an electronic control hydraulic distributor designed to regulate the flow of pressurized oil from and towards the hydraulic actuator, in such a way as to control movement of the valve between the closed and maximum opening position.
To satisfy pressurized oil requirements, the combustion engines currently being tested are furthermore provided with a hydraulic circuit that comprises an oil collection tank, inside which the oil to be conveyed to the actuators is stored at ambient pressure, and a pumping unit designed to convey pressurized oil to the various hydraulic distributors, taking it directly from the collection tank.
Each electronic control hydraulic distributor is connected to the hydraulic circuit in such a way as to establish direct communication, respectively, between the corresponding linear hydraulic actuator and the pumping unit delivery inlet when it is necessary to move the valve from the closed position to the maximum opening position, and the collection tank when it is necessary to move the valve from the maximum opening position to the closed position. In the first case, the pressurized oil is conveyed into the linear hydraulic actuator whereas in the second case the pressurized oil that fills the linear hydraulic actuator is conveyed directly into the collection tank.
In other words, therefore, all the pressurized oil conveyed inside the hydraulic actuator during movement of the valve from the closed position to the maximum opening position is discharged directly into the collection tank during movement of the valve from the maximum opening position to the closed position, propelled by the elastic element designed to keep the valve in the closed position.
The main disadvantage of the solution described above is the considerable amount of pressurized oil required which increases proportionally to the engine rpm, and which calls for the use of pumping units that are so bulky as to be incompatible with use in automotive applications.
To solve the above problem, the applicant has developed and patented a combustion engine in which the electrohydraulic operating device is able to re-convey, during movement of the valve from the maximum opening position to the closed position, the majority of the pressurized oil present inside the hydraulic actuator into the high pressure part of the hydraulic circuit, exploiting the elastic energy accumulated by the elastic element designed to keep the valve in the closed position.
In other words, the linear hydraulic actuator and the corresponding electronic control hydraulic distributor are constructed and driven in such a way as to re-pump, during movement of the valve from the maximum opening position to the closed position, the majority of the pressurized oil present inside the hydraulic actuator into the high pressure part of the hydraulic circuit, exploiting the elastic energy accumulated by the elastic element designed to keep the valve in the closed position.
In this way, the overall pressurized oil requirements are drastically reduced, making it possible to use small pumping units compatible with automotive use. The pressurized oil re-pumped by each linear hydraulic actuator into the high pressure part of the hydraulic circuit can be immediately reused.
Unfortunately, the last solution described above requires the use of particularly complicated electrohydraulic devices which are not currently compatible with the automotive sector due to cost and reliability.
The aim of the present invention is to produce an electrohydraulic device to operate the valves of a combustion engine which is more reliable and cheaper to produce than those currently known, so that it can be effectively used in the automotive sector.
According to the present invention, an electrohydraulic device is produced for the operation of at least one intake or exhaust valve of a combustion engine; the electrohydraulic device comprises a linear hydraulic actuator, which is designed to move said valve axially from a closed position to a maximum opening position, and an electronic control hydraulic distributor designed to regulate the flow of pressurized liquid from and towards the linear hydraulic actuator, in such a way as to control movement of said valve between said closed and maximum opening positions; the electrohydraulic device is characterized in that said electronic control hydraulic distributor comprises a slide valve which, by selection, can be set to a first operating position in which it establishes direct communication between said linear hydraulic actuator and an outlet of the pressurized liquid, a second operating position in which it isolates said linear hydraulic actuator in such a way as to prevent the flow of pressurized liquid from or towards the actuator, and a third operating position in which it establishes direct communication between said linear hydraulic actuator and an inlet of the pressurized liquid.